Cosmic Ray-Modified Astrophysical Shocks: Modeling and Observations

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The current dominant paradigm in cosmic ray (CR) research says that the bulk of Galactic CRs with energies below a peta-electron volt are created in supernova remnants (SNRs) via diffusive shock acceleration. This is now at a turning point: soon, the comparison between theoretical calculations and observations from the radio band to gamma rays to high energy neutrinos is expected to either confirm the paradigm or call for a paradigm shift. This project will develop novel theoretical and observational techniques to test the SNR paradigm. The theoretical studies are based around a common theme: how do cosmic rays modify the structure of the shock? The work will investigate magnetic field amplification, injection and acceleration of CRs, and the role of dust sputtering and the large neutral component in the upstream plasma. Analysis of neutral hydrogen in the so-called Balmer-dominated shocks should lead to a novel way to measure the shock acceleration efficiency. The research will include consideration of how cosmic rays escape their acceleration sites and propagate towards the Earth and of the kinetic diffusion of CRs. Modeling of time- and spatially-dependent particle dynamics will be compared with observed non-thermal filaments and tied to the results of high energy particle observations.This is a multidisciplinary project involving data analysis and theoretical and computational work in astrophysics and plasma physics. Work with students in the Purdue Computer Graphics Technology Department will lead to an interactive kiosk, in partnership with Purdue's Discovery Learning Center, to explain about CRs to all visiting groups, including K-12 students, teachers, and the general public.